Recently, with advances and improvements in communication standards, hardware, and OSs, wireless information communication networks have been generalized. As more users have used information devices in the form of being used during movement, e.g., notebook PCs, PDAs, and cell phones, radio has been becoming an indispensable infrastructure in constructing an information communication network. Consider, for example, a case wherein when holding a meeting, each participant brings an information terminal to the meeting to form a temporary network which allows only the participants in the meeting room to share information. Consider also a case wherein information devices existing in a limited range (e.g., a floor, room, or section) in a building accommodating a plurality of offices share information. Applying wired network connection to these cases makes it necessary to redo interconnection every time devices change. This makes it difficult to form a network. In contrast to this, information devices capable of wireless communication can share information without redoing interconnection as long as wireless access points exist.
Japanese Patent Laid-Open No. 2004-046855 discloses an arrangement which allows transmission/reception of information upon automatic wireless connection. In addition, Japanese Patent Laid-Open No. 11-196029 discloses a method in which in forming a plurality of subgroups by radio, a given child device participates in a subgroup by outputting a grouping request to a parent device when entering a place at a given position. Both of these techniques use wireless communication to improve usability.
An information communication network using radio waves, however, does not allow to visually check the reachable range of radio waves, and hence requires security management stricter than that for a conventional wired information communication network. Challenges for an information communication network using radio waves, in particular, are to safely distribute keys for the encryption of communication and prevent tapping caused by spoofing using a key acquired once. Japanese Patent Laid-Open Nos. 2004-046855 and 11-196029 give no consideration to such challenges.
With regard to radio techniques and security, Japanese Patent Laid-Open No. 2004-032336 discloses a method in which when, for example, a user accesses a file in a server by using a portable information terminal, a position and a time zone where the user can access the file is registered in the server in advance. Although this method describes access right to a file, it does not describe communication encryption. For this reason, in an in-house wireless LAN or the like, intercepting radio waves makes it possible to acquire information with no access right. The scheme of registering, with a server in advance, a position and a time at which a given user can access the server is not suitable for an application designed to safely exchange information within a group formed by temporary members as in a meeting, because there are too many setting items.
With regard to position measurement techniques, there has been proposed a method based on GPS, a method which can measure a position more accurately by also using radio waves from a base station than by using GPS, and a method of measuring a position by using the difference in arrival time between radio waves from a wireless access point. In addition, there have been proposed various methods, e.g., a method using an apparatus which causes a fluorescent lamp to emit infrared light to transfer a position.
Under the circumstances, conventional radio techniques are required to be in the form of allowing users to secure ranges, which have been obscure, by using position measurement techniques. Furthermore, such techniques are required to simply prevent tapping by safely distributing keys to a temporary group and simply prevent spoofing using a previously acquired key by updating the key.